This is something I've been thinking about lately, especially after watching the anime a bit. I love Jinbe (called Jimbei in English, apparently), I would love to see him join the Straw Hat Pirates. He's a Fishman, for one thing, and having a Fishman in the crew would definitely be useful. Not to mention his Fishman Karate techniques are awesome, and powerful (but thanks to the 2-year power-up, I think Luffy, Zoro, and even Sanji might be stronger then him). He's also spent quite a bit of time with Luffy, he's bonded with him, he helped pull Luffy out of his sorrow by reminding him of his crew. We even get a flashback, with 2 important people in his life dying.
Still not sure about some other things, though, like what kind of role he would play in the crew... He could be a fighter, or a helmsman. I've seen that as a role needed to be filled for the Straw Hat Pirates, only it wasn't as important as any of the other ones.
I'm also not exactly sure what he dream would be... Although, if I recall correctly, Ace asked him, while still imprisoned, to look after Luffy when/if he dies. Jinbe said that he won't help anyone he doesn't like, but he's made it clear that he's willing to die for Luffy. Still, I don't think that would be enough of a reason for him to join the Straw Hat Pirates...
I also find it weird that a former captain and Warlord would join Luffy's crew as an underling... Okay, that's not the case at all with the Straw Hat Pirates, but he'll still basically serve under him. Maybe he cant be Luffy's calming agent, like when he was upset about Ace's death. For some reason, their fight about going to beat up Hody Jones also sticks out in my mind, for some reason. It's like they're not even crewmates and they're already fighting.
I don't know, it doesn't make sense. I'd like to see it happen, but I can understand if it doesn't... I'd STILL like to see Surume join the crew as their pet, though. He'd be useful in the eventual fight against the Blackbeard Pirates, since they have someone who's just as big!